american hand book of the daguerreotype-第10部分

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n　connection　with　the　Accelerators。

＇page　86＇

Iodides。The　iodide　treated　with　the　oil　of　vitriol；　instantly　produces　a　considerable　deposit　of　iodine；　and　if　the　mixture　be　heated；　intense　violent　vapors　are　disengaged。　The　reaction　is　due　to　the　decomposition　of　oil　of　vitriol　by　iodohydric　acid；　water　and　sulphurous　acid　being　formed；　and　iodine　set　free。　　The　iodides　in　solution　are　decomposed　by　chlorine；　iodine　being　precipitated；　the　smallest　quantity　of　which　in　solution　is　instantly　detected　by　its　imparting　to　starch　an　intensely　blue　color。

Iodide　of　Potassium。*This　compound　is　easily　made　in　the　following　manner：　Subject　to　a　moderate　heat　a　mixture　of　100　parts　of　iodine；　75　of　carbonate　of　potash；　30　of　iron　filings；　and　120　parts　of　water。　This　mass　must　be　thoroughly　dried　and　then　heated　to　redness；　the　resulting　reddish　powder　is　to　be　washed　with　water；　and　the　solution　obtained　filtered；　and　evaporated　to　dryness。　It　is　found　that　100　parts　of　iodine　yield　135　parts　of　very　white；　but　slightly　alkaline；　iodide　of　potassium。

*　I　shall　present　the　preparation　of　only　a　few　iodides；　and　such　as　are　more　intimately　connected　with　the　Daguerreotype。

Experiment。On　projecting　dry　pulverized　iodide　of　potassium　into　fused　anhydrous　phosphoric　acid；　a　violent　disengagement　of　iodine　takes　place；　attended　by　a　transient　ignition；　fused　hydrate　of　phosphoric　acid　liberates　iodine　abundantly　from　iodide　of　potassium；　this　reaction　is　accompanied　by　the　phenomenon　of　flame　and　formation　of　a　considerable　quantity　of　hydriodic　acid。

Iodide　of　Mercury。For　the　preparation　of　iodide　of　mercury；　Dublanc　recommends　to　cover　100　grms。　　of　mercury　with　1　kilogrm。　of　alcohol；　to　add　124　grms。　　of　iodine　gradually　in　portions　of　ten　grms。；　and　agitating　between　each　fresh　addition；　until　the　alcohol　becomes　colorless　again。　　After　the　addition　of　the　last　4　grms。　the　alcohol　remains　colored；　the　whole　of　the　mercury　having　become　converted　into　iodide。　　The　resulting　preparation　is　washed　with　alcohol；　it　is　crystalline　and　of　a　hyacinth　color。

Iodide　of　Silver。This　compound　is　formed　upon　every　plate　upon　which　a　Daguerreotype　is　produced。　　The　vapor　of　iodine　coming　in　contact　with　the　silver　surface；　forms　an　iodide　which　is　peculiarly　sensitive　to　light。

The　various　colors　produced　are　owing　to　the　thickness　of　the　coating；　and　the　maximum　sensibility　of　the　coating；　as　generally　adopted；　is　when　it　assumes　a　deep　yellow；　or　slightly　tinged　with　rose　color。

This　compound　is　largely　employed　in　most　photographic　processes　on　paper；　and　may　be　easily　prepared　by　the　following　formula：　By　adding　iodide　of　potassium　to　a　solution　of　nitrate　of　silver；　a　yellowish…white　precipitate　of　iodide　of　silver　is　obtained；　which　is　insoluble　in　water；　slightly　soluble　in　nitric　acid；　and　soluble　in　a　small　degree　in　ammonia；　which　properties　seem　easily　to　distinguish　it　from　the　chloride　and　bromide　of　silver。　Chlorine　decomposes　it　and　sets　the　iodine　free；　and　chlorohydric　acid　converts　it　into　a　chloride。　　It　fuses　below　a　red　heat。　Although　the　effect　of　light　on　the　iodide　is　less　rapid　than　on　the　chloride；　the　former　sooner　turning　black；　assuming　a　brown　tinge；　but　when　in　connection　with　gallic　acid　and　the　ferrocyanate　of　potash；　it　forms　two　of　the　most　sensitive　processes　on　paper。

Iodide　of　silver　dissolves　easily　in　a　solution　of　iodide　of　potassium；　and　the　liquid　deposits　in　evaporation　crystals　of　a　double　iodide。

Iodide　of　Gold。If　a　solution　of　potassium　be　added　to　a　solution　of　chloride　of　gold；　a　precipitate　of　iodide　of　gold　takes　place；　soluble　in　an　excess　of　the　precipitate。　A　little　free　potash　should　be　added　to　combine　with　any　iodide　that　may　chance　to　be　set　free　by　the　chloride　of　gold。

Iodide　of　Lime　is　prepared　by　adding　iodine　to　hydrate　of　lime　（which　will　be　referred　to　farther　on）　until　the　mixture　assumes　a　light　yellow　shade；　when　wanted　for　combinations　with　accelerators；　or　to　a　dark　brown　when　employed　for　the　first　coating。　This　latter　mixture　has　been　sold　in　our　market　under　the　name　of　〃Iodide　of　Brome。〃

Iodide　of　Bromine。（See　page　76。）

Experiments　with　Iodine。Place　a　plate　which　bas　been　exposed　in　the　camera　over　the　vapor　of　iodine　for　a　very　brief　period；　and　it　will　present　the　appearance　of　the　impression　having　been　solarized。

b。　　Upon　a　Daguerreotype　plate；　from　which　an　impression　has　been　effaced　by　rubbing　or　otherwise；　the　picture　may　be　made　to　reappear　by　merely　coating　it　over　with　iodine。

c。　　Place　in　a　vessel　a　little　water；　into　which　put　the　smallest　possible　quantity　of　free　iodine　and　add　a　little　starch；　and　the　liquid　will　instantly　assume　a　blue　color。　　Advantage　is　taken　of　this　fact　in　the　laboratory　to　detect　the　presence　of　iodine　in　liquids。　The　starch　should　be　dissolved　in　boiling　water　and　allowed　to　cool。　There　are　numerous　other　interesting　experiments　that　can　be　performed　by　the　aid　of　iodine；　but　it　is　unnecessary　here　to　consume　more　space。


CHLORINE。

History。The　Swedish　chemist；　Scheele；　in　1774；　while　examining　the　action　of　hydrochloric　acid　on　peroxide　of　manganese；　first　noticed　this　element。　He　called　it　dephlogisticated　muriatic　acid。　　It　was　afterwards；　by　the　French　nomenclaturists；　termed　oxygenated　muriatic　acid；　conceiving　it　to　be　a　compound　of　oxygen　and　muriatic　acid。　This　view　of　its　notice　was　corrected　by　Sir　H。　Davy　（in　1809）；　who　gave　it　the　present　name。　　In　1840…41；　this　gas　vas　employed　for　accelerating　the　operation　of　light　upon　the　iodized　Daguerreotype　plate。　John　Goddard；　Wolcott　&　Johnson；　Claudet；　Draper；　Morse　and　others；　were　among　the　first　made　acquainted　with　its　use。　　Count　Rumford；　Ritter；　Scheele；　Seebert　and　others；　experimented　with　chlorine　in　regard　to　its　effect　when　exposed　to　the　action　of　light　in　combination　with　silver。　In　1845；　M。　Edward　Becquerel　announced　that　he　had　〃been　successful　in　obtaining；　by　the　agency　of　solar　radiations；　distinct　impressions；　of　the　colors　of　nature。〃

On　the　4th　of　March；　1851；　Neipce；　St。　Victor；　a　former　partner　of　DAGUERRE；　announced　that　he　had　produced　〃all　the　colors　by　using　a　bath　of　bichloride　of　copper；　and　that　a　similar　phenomenon　occurs　with　all　salts　of　copper；　mixed　with　chlorine。〃

Preparation。This　is　easily　accomplished　by　putting　about　two　parts　of　hydrochloric　（muriatic）　acid　on　one　of　powdered　black　oxide　of　manganese；　and　heating　it　gradually　in　a　flask　or　retort；　to　which　may　be　adapted　a　bent　glass　tube。　A　yellowish…green　gas　is　disengaged；　which　being　conducted　through　the　glass　tube　to　the　bottom　of　a　bottle；　can　readily　be　collected；　being　much　heavier　than　the　air；　displaces　it　completely　and　the　bottle　is　filled　（which　can　be　seen　by　the　green　color）；　a　greased　stopper　is　tightly　fitted　to　it；　and　another　bottle　may　be　substituted。

In　all　experiments　with　chlorine；　care　should　be　taken　not　to　inhale　the　gas！

Properties。Chlorine　is　a　greenish…yellow　gas　（whence　its　name；　from　chloros；　green）；　with　a　powerful　and　suffocating　odor；　and　is　wholly　irrespirable。　Even　when　much　diluted　with　air；　it　produces　the　most　annoying　irritation　of　the　throat；　with　stricture　of　the　chest　and　a　severe　cough；　which　continues　for　hours；　with　the　discharge　of　much　thick　mucus。　The　attempt　to　breathe　the　undiluted　gas　would　be　fatal；　yet；　in　a　very　small　quantity；　and　dissolved　in　water；　it　is　used　with　benefit　by　patients　suffering　under　pulmonary　consumption。

Under　a　pressure　of　about　four　atmospheres；　it　becomes　a　limpid　fluid　of　a　fine　yellow　color；　which　does　not　freeze　at　zero；　and　is　not　a　conductor　of　electricity。　　It　immediately　returns　to　the　gaseous　state　with　effervescence　on　removing　the　pressure。

Water　recently　boiled　will　absorb；　if　cold；　about　twice　its　bulk　of　chlorine　gas；　acquiring　its　color　and　characteristic　properties。　The　moist　gas；　exposed　to　a　cold　of　32　deg。；　yields　beautiful　yellow　crystals；　which　are　a　definite　compound　of　one　equivalent　of　chlorine　and　ten　of　water。　If　these　crystals　are　hermetically　sealed　up　in　a　glass　tube；　they　will；　on　melting；　exert　such　a　pressure　as　to　liquefy　a　portion　of　the　gas；　which　is　distinctly　seen　as　a　yellow　fluid；　not　miscible　with　the　water　which　is　present。　　chlorine　is　one　of　the　heaviest　of　the　gases；　its　density　being　2。47；　and　100　cubic　inches　weighing　76。5　grains。

Chlorine　Water。This　combination；　which　is　used　in　conducting　M。　Neipce's　process；　can　be　readily　prepared　by　conducting　the　gas　into　a　bottle　containing　distilled　water。　One　part　water　dissolves　two　parts　of　chlorine。

Chlorides。The　metallic　chlorides　are　nearly　all　soluble　in　water；　that　of　silver　and　protochloride　of　mercury　being　the　only　exceptions。　A　metallic　chloride；　treated　with　oil　of　vitriol；　disengages　chlorohydric　acid。　　Heated　with　a　mixture　of　peroxide　of　manganese　and　sulphuric　acid；　chlorine　is　given　off；　which　is　easily　recognized　by　its　odor　and　other　physical　properties。

The　chlorides　dissolve　in　water；　give　with　nitrate　of　silver；　a　white　precipitate；　even　in　highly　diluted　solutions；　becoming　violet　colored　and　finally　black　when　exposed　to　the　light。　　The　rapidity　of　the　change　of　color　is　proportioned　to　the　intensity　of　the　light。　It　is　insoluble　in　nitric　acid；　but　readily　soluble　in　ammonia；　it　fuses　without　decomposition；　forming；　when　cold；　a　tough；　horny　mass；　and　is　reduced　by　hydrogen　and　by　fusion　with　carbonate　of　soda；　or　with　resin。

Chloride　of　Bromine。　　（See　page　74。）

Chloride　of　Iodine。　　（See　page　85。）

Chloride　of　potassium。or　（Muriate　of　Potassa）。Dissolve　half　an　ounce　of　carbonate　of　potassa　in　water；　and　neutralize　with　muriatic　acid。　Upon　concentrating　the　solutions；　cubic　crystals　will　be　obtained；　having　a　taste　similar　to　common　salt。　　They　consist　of　potassium　and　chloride；　and　when　dissolved　in　water　they　may　be　regarded　as　muriate　of　potassa。

Chloride　of　Lime。Mix　half　an　ounce　of　slacked　lime　（hydrate　of　lime）　with　six　ounces　of　water；　and　conduct　into　this　milk　of　lime；　with　frequent　agitation；　as　much　chlorine　gas　as　will　evolve　from　two　ounces　of　muriatic　acid　and　half　an　ounce　of　black　oxide　of　manganese。　The　liquid　clarifies　by　standing；　may　be　regarded　as　a　solution　of　chloride　of　lime；　and　must　be　protected　from　the